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AN37.1-3 | Cavity of Nose — Self-Directed Learning
CLINICAL SCENARIO
A 35-year-old painter from Chennai presents with a 3-month history of right-sided nasal obstruction, foul-smelling nasal discharge, right cheek numbness, and loose right upper teeth. CT of the paranasal sinuses shows a soft-tissue mass in the right maxillary sinus with erosion of the medial and anterior walls.
Why do maxillary sinus tumours cause cheek numbness and loose teeth? Which branches of which cranial nerve are involved? Why are maxillary sinus cancers often detected late? What is Ohngren's line and why does it matter?
The answers require a precise understanding of the boundaries of the maxillary sinus and the structures it sits between. This module will make you confident in diagnosing and conceptualising ENT and maxillofacial emergencies, from epistaxis to sinus carcinoma.
WHY THIS MATTERS
The nasal cavity and paranasal sinuses are directly relevant to several high-burden conditions in India:
- Epistaxis — one of the most common ENT emergencies; the anatomy of Little's area is essential for cauterisation
- Chronic rhinosinusitis — affects ~14% of the Indian population; allergic fungal sinusitis is particularly common in humid climates
- Allergic rhinitis — affects 20–30% of Indians; the nasal turbinates and their rich blood supply are central
- Maxillary sinus carcinoma — India has relatively high incidence (woodworkers, leather workers, farmers); often presents late
- Functional Endoscopic Sinus Surgery (FESS) — the primary surgical treatment for chronic sinusitis; requires precise knowledge of the ostiomeatal complex and the orbit/skull base relations
- Complications of sinusitis: orbital cellulitis, intracranial extension — life-threatening if missed
RECALL
Before we begin, recall:
- The nasal cavity is divided by the nasal septum (bony posteriorly, cartilaginous anteriorly)
- The nasal cavity communicates anteriorly with the exterior via the nares (nostrils) and posteriorly with the nasopharynx via the choanae
- The nerve supply of the nasal cavity comes from CN V1 (anterior/superior) and CN V2 (posterior/inferior) with contributions from the olfactory nerve (CN I) for smell
- The paranasal sinuses are air-filled extensions of the nasal cavity into the surrounding bones
Nasal Septum and Lateral Wall of Nose (AN37.1)
Nasal septum — components:
| Part | Bones/Cartilages |
|---|---|
| Anterosuperior | Septal cartilage (quadrilateral cartilage) |
| Posterosuperior | Perpendicular plate of the ethmoid bone |
| Posteroinferior | Vomer (the keel-shaped bone) |
| Floor | Nasal crest of maxilla and palatine bone |
Deviated nasal septum (DNS): Very common in the Indian population. Most deviations occur at the junction of the vomer and the septal cartilage (a cartilage-bone junction). Causes nasal obstruction, mouth breathing, epistaxis.
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Lateral wall of the nose — turbinates (conchae):
- Inferior turbinate (concha): separate bone; largest; most clinically significant
- Middle turbinate: part of ethmoid bone; the ostiomeatal complex (OMC) lies under it
- Superior turbinate: part of ethmoid; smallest
- Supreme turbinate: may be present (variant)
Meatuses (spaces under each turbinate):
| Meatus | What drains here |
|---|---|
| Inferior meatus | Nasolacrimal duct (opens 1.5 cm posterior to the anterior end of the inferior turbinate) |
| Middle meatus | Maxillary, frontal, and anterior ethmoidal sinuses (via the ostiomeatal complex/hiatus semilunaris) |
| Superior meatus | Posterior ethmoidal sinuses |
| Sphenoethmoidal recess (above superior turbinate) | Sphenoidal sinus |
Ostiomeatal complex (OMC): The key functional unit:
- Consists of: uncinate process + infundibulum + hiatus semilunaris + bulla ethmoidalis (anterior ethmoid air cells)
- All three major sinuses (maxillary, frontal, anterior ethmoid) drain through the OMC
- Obstruction of the OMC → chronic sinusitis (common pathway)
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Blood supply of the nasal cavity:
| Artery | Origin | Area |
|---|---|---|
| Anterior ethmoidal artery | Ophthalmic artery (ICA) | Anterosuperior nasal septum + lateral wall |
| Posterior ethmoidal artery | Ophthalmic artery (ICA) | Posterosuperior nasal septum + lateral wall |
| Sphenopalatine artery | Maxillary artery (ECA) | Posterior nasal cavity — the largest nasal artery; the main supply to the inferior turbinate |
| Greater palatine artery | Maxillary artery (ECA) | Floor of nasal cavity |
| Septal branch of superior labial artery | Facial artery (ECA) | Anterior nasal septum |
Little's area (Kiesselbach's plexus):
- Anteroinferior part of the nasal septum
- Anastomosis of 5 arteries: anterior ethmoidal + posterior ethmoidal + sphenopalatine + greater palatine + superior labial
- 90% of all epistaxis originates here (anterior epistaxis)
- Treatment: cauterisation (silver nitrate or bipolar) or nasal packing
- Posterior epistaxis (10%): from sphenopalatine artery territory; more severe; older patients; treated by posterior nasal packing or endoscopic ligation of the sphenopalatine artery
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Nerve supply:
| Nerve | Origin | Area |
|---|---|---|
| Olfactory (CN I) | Olfactory bulb | Olfactory mucosa (upper 1/3 of septum + opposite lateral wall) |
| Anterior ethmoidal nerve | Nasociliary (CN V1) | Anterosuperior cavity, tip of nose |
| Posterior nasal nerves | Pterygopalatine ganglion (CN V2) | Posterior 2/3 of nasal cavity |
| Nasopalatine nerve | Pterygopalatine ganglion (CN V2) | Nasal septum → palate via incisive foramen |
Paranasal Sinuses — Location and Functional Anatomy (AN37.2)
Overview: 4 pairs of paranasal sinuses, all communicate with the nasal cavity. Functions: humidify and warm inspired air, lighten the skull, resonate the voice, provide a 'crumple zone' for facial trauma.
Maxillary sinus (antrum of Highmore):
- Largest sinus; within the body of the maxilla
- Floor: alveolar process of maxilla — roots of upper molars (especially 2nd premolar, 1st molar) may project into the floor → dental pain mimicking sinusitis, or oro-antral fistula after tooth extraction
- Roof: floor of the orbit — orbital cellulitis is a complication of maxillary (and ethmoidal) sinusitis
- Medial wall: lateral wall of the nasal cavity; ostium opens HIGH on the medial wall into the middle meatus (hiatus semilunaris) — poor drainage in the upright position (ostium is near the roof of the sinus, so secretions pool at the floor)
- Posterior wall: infratemporal fossa (pterygopalatine fossa behind)
Frontal sinus:
- In the frontal bone above the medial part of the orbital margin
- Drains via the frontonasal duct into the middle meatus
- Absent at birth, develops at 2 years, reaches adult size by puberty
Ethmoidal sinuses (ethmoid air cells):
- Anterior ethmoidal cells: drain into middle meatus (via OMC)
- Posterior ethmoidal cells: drain into superior meatus
- Lateral wall = lamina papyracea (paper-thin): immediately medial to the orbit → orbital complications of ethmoidal sinusitis
- Roof = cribriform plate + fovea ethmoidalis: adjacent to the anterior cranial fossa → intracranial complications
Sphenoidal sinus:
- Within the body of the sphenoid bone
- Drains into the sphenoethmoidal recess
- Relations (all immediately adjacent): pituitary gland (superior), optic chiasm (superior-anterior), cavernous sinus (lateral, with ICA and CN III, IV, V1, V2, VI inside), CN II (lateral)
- Transsphenoidal pituitary surgery approaches the pituitary via the sphenoidal sinus
SELF-CHECK
A. The ostium is too small for normal cilia to function
B. The ostium position near the roof of the sinus means secretions pool at the floor and cannot drain by gravity in the upright or lying position
C. The ostium is blocked by the middle turbinate
D. Maxillary sinus secretions are too viscous for ciliary clearance
Reveal Answer
Answer: .
The maxillary sinus ostium is located near the roof of the sinus on its medial wall (high position). This means secretions accumulate at the floor of the sinus and cannot drain by gravity when the person is upright. Ciliary transport must actively move secretions upward to the ostium — any mucosal oedema impairs this, leading to retained secretions and chronic infection. This is the main anatomical reason maxillary sinusitis is so persistent.
Anatomical Basis of Sinusitis and Maxillary Sinus Tumours (AN37.3)
Acute sinusitis — anatomical considerations:
- Most sinusitis follows a viral upper respiratory infection that causes mucosal oedema → blocks the sinus ostia → retained secretions → secondary bacterial infection
- Bacterial causes in India: Streptococcus pneumoniae (most common), Haemophilus influenzae; fungal sinusitis (Aspergillus, Mucor) in diabetics or immunocompromised patients
- Chronic sinusitis: defined as >12 weeks of symptoms; strongly linked to OMC obstruction
Complications of sinusitis (anatomically determined):
| Complication | Anatomical route |
|---|---|
| Orbital cellulitis / abscess | Ethmoidal sinusitis via lamina papyracea, or maxillary via orbital floor |
| Intracranial (meningitis, abscess, cavernous sinus thrombosis) | Frontal sinus (posterior wall) or ethmoidal (fovea ethmoidalis/cribriform plate); cavernous sinus from sphenoidal sinus |
| Cavernous sinus thrombosis | Dangerous — high mortality; presents with proptosis + chemosis + ophthalmoplegia + sepsis |
| Osteomyelitis of frontal bone (Pott's puffy tumour) | Frontal sinus infection erodes into the outer table → subperiosteal abscess → fluctuant scalp swelling |
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Maxillary sinus carcinoma — clinical anatomy (AN37.3):
Early symptom-free period: the sinus is large; tumour grows within it without causing symptoms → late presentation (common in India where patients present late).
Ohngren's line: an imaginary line from the medial canthus of the eye to the angle of the mandible. Divides the maxillary sinus into:
- Anteroinferior (infrastructure): better prognosis (presents earlier — involves alveolus, palate)
- Superoposterior (suprastructure): worse prognosis (involves orbit, pterygoid plates, pterygomaxillary fissure, skull base)
Symptoms by wall involvement:
| Wall Eroded | Symptom |
|---|---|
| Medial wall (nasal) | Nasal obstruction, epistaxis, unilateral mucopurulent discharge |
| Floor (alveolar) | Loose upper teeth, oro-antral fistula |
| Roof (orbital floor) | Proptosis, diplopia (upward gaze deficit if inferior rectus tethered), cheek and lower eyelid anaesthesia (infraorbital nerve, CN V2) |
| Anterior wall | Cheek swelling, numbness of cheek and upper lip (infraorbital nerve V2) |
| Posterior wall | Trismus (pterygoid muscle involvement), bulge in cheek |
Infraorbital nerve (CN V2): exits via the infraorbital foramen on the anterior wall of the maxilla → supplies: cheek, lower eyelid, lateral nose, upper lip, anterior upper teeth. Numbness in this distribution = anterior wall maxillary sinus involvement.
SELF-CHECK
A. Facial nerve (CN VII) — buccal branch
B. Infraorbital nerve and posterior superior alveolar nerve (branches of CN V2)
C. Lingual nerve (CN V3)
D. Buccal nerve (CN V3)
Reveal Answer
Answer: .
The infraorbital nerve (CN V2) exits through the infraorbital foramen on the anterior wall of the maxillary sinus, supplying the cheek, lower eyelid, and upper lip. The posterior superior alveolar nerve (also CN V2) supplies the upper molars and premolars. Maxillary sinus carcinoma eroding the anterior/inferior walls directly compresses or invades these V2 branches → cheek anaesthesia and dental symptoms.
SELF-CHECK
A. The cribriform plate (to avoid intracranial entry)
B. The lamina papyracea (to avoid orbital injury)
C. The uncinate process (to preserve OMC drainage)
D. The middle turbinate (to maintain olfaction)
Reveal Answer
Answer: .
The lamina papyracea (orbital lamina of the ethmoid) is the paper-thin lateral wall of the ethmoid labyrinth, immediately medial to the orbital contents. Breach during FESS causes orbital fat herniation, orbital haemorrhage, or extraocular muscle damage. The cribriform plate (roof) is also critical but lies superiorly; the lamina papyracea is the lateral boundary. Both must be respected in FESS.
CLINICAL PEARL
Cavernous sinus thrombosis — an ENT/neurosurgical emergency: The sphenoidal sinus is immediately lateral to the cavernous sinus. Spread of sphenoidal or ethmoidal sinusitis into the cavernous sinus causes septic cavernous sinus thrombosis — one of the most feared complications of sinusitis. Presentation: high fever + severe headache + rapidly progressive proptosis + chemosis + ophthalmoplegia (all extraocular movements affected as CN III, IV, VI run in the cavernous sinus wall/sinus) + signs of meningism. Furunculosis of the nose (danger triangle of the face): a boil on the nose or central face can spread via the facial vein → angular vein → ophthalmic vein → cavernous sinus. Never squeeze a nasal or central facial boil — teach this to your patients.
REFLECT
KEY TAKEAWAYS
Cavity of the Nose — Key Points:
- Nasal septum: septal cartilage (anterior) + perpendicular plate of ethmoid (posterosuperior) + vomer (posteroinferior); DNS most common at cartilage-vomer junction
- Turbinates and meatuses: inferior meatus = nasolacrimal duct; middle meatus = maxillary + frontal + anterior ethmoid (via OMC); superior meatus = posterior ethmoid; sphenoethmoidal recess = sphenoidal sinus
- Ostiomeatal complex (OMC): uncinate + infundibulum + hiatus semilunaris + ethmoid bulla; blockage → chronic sinusitis
- Little's area (Kiesselbach's plexus): anteroinferior septum; 5-artery anastomosis (ethmoidal + sphenopalatine + greater palatine + superior labial); 90% of epistaxis; cauterise here first
- Posterior epistaxis: sphenopalatine artery; severe, elderly; treat by posterior packing or endoscopic sphenopalatine artery ligation
- Maxillary sinus: ostium high on medial wall → poor gravity drainage; floor = upper molar roots; roof = orbital floor; posterior wall = pterygopalatine fossa
- Sphenoidal sinus: relations — pituitary (superior), optic chiasm (ant-superior), cavernous sinus (lateral with ICA + CN III IV V1 V2 VI)
- Maxillary sinus carcinoma: Ohngren's line divides into infra- (better) and suprastructure (worse); infraorbital nerve involvement → cheek numbness; floors erosion → loose teeth; late presentation = common